Light produced from an object existing in nature may have characteristic values represented in units based on wavelength. An image sensor is an apparatus that may pick up an image of an object by using the properties of a semiconductor device responsive to external energy. A pixel of an image sensor may detect light produced from an object and may convert it into an electrical value.
Such an image sensor may be classified into a charge coupled device (CCD) based on silicon semiconductor and a complementary metal oxide semiconductor (CMOS) image sensor fabricated by a submicron CMOS fabrication technology. Of these image sensors, the CCD is a device in which charge carriers may be stored in a capacitor and transferred under the situation that each MOS capacitor may be relatively closely disposed to each other. However, the CCD may have various disadvantages, such as relatively complicated drive mode, relatively high power consumption, impracticality of integrating a signal processing circuit in a chip for the CCD due to many mask processes and other practical reasons. To overcome these disadvantages, many studies may have been done for the development of CMOS image sensors.
A CMOS image sensor may obtain an image by forming a photodiode (PD) and a MOS transistor within a unit pixel to detect signals in a switching mode. The CMOS image sensor may have advantages of relatively low manufacturing costs and relatively low power consumption and being relatively easily integrated into a peripheral circuit chip compared to a CCD. As mentioned above, since the CMOS image sensor may be produced using a CMOS fabrication technology, the CMOS image sensor may be easily integrated into a peripheral system for performing operations such as amplification and signal processing, resulting in relatively minimized manufacturing costs. Also, the CMOS image sensor has a relatively rapid processing speed and a relatively low power consumption which corresponds to about 1% of power consumption of the CCD.
Due to relatively high demand for image sensors with relatively high resolution, development of CMOS fabrication processes has resulted in minimization of a size of a unit pixel of an image sensor. With the unit pixels minimized in size, a distance between photodiodes of adjacent unit pixels may become closer, which may contribute to a crosstalk occurrence frequency between adjacent pixels.
To lower the crosstalk between the adjacent pixels, methods for maximizing light blocking characteristics of a device isolation film disposed between the unit pixels may be used in the related art.
FIG. 1 is an arrangement view showing a pixel array structure of an image sensor, to which a related art method for relatively lowering a crosstalk occurrence frequency may be applied, in accordance with embodiments. FIG. 2 is a cross sectional view taken along the line II-II′ of FIG. 1.
According to related art, as shown in FIGS. 1 and 2, a plurality of trenches may be formed on a semiconductor substrate 30 to isolate photodiodes 10 from each other. A plurality of device isolation regions 20 may be formed within the trenches, each of the device isolation regions 20 may be formed by forming a first device isolation film 21 along a trench surface, and then forming a second device isolation film 23 in the first device isolation film 21 to block light incident from adjacent photodiodes 10. The second device isolation film 23 may be formed as an optical absorption film for absorbing incident light from the adjacent photodiodes 10 to minimize crosstalk generated between pixels.
However, in order to implement an image with relatively higher resolution, the photodiodes of the adjacent unit pixels should be closer to each other. Also, the device isolation films may be reduced in width, and thus may end up with unsatisfactory light blocking characteristics. Moreover, according to the related art, the process of forming the device isolation films by burying trenches may be divided into the process of forming the first device isolation film 21 and the process of forming the second device isolation film 23, which may contribute to the cost associated with a relatively high number of processes, which may thereby undesirably minimize production yield.